The zip above contains both the Pixel Launcher and the Wallpaper picker APKs. Unzip them, then install through a file manager.

Note: If you want the Google Now launcher pane to work, you'll have to install the launcher APK to /system (mount the /system partition r/w and copy, or wait for a flashable zip). If you've already previously done this to the Nexus Launcher, then all you need to do now is install the Pixel Launcher APK as an update - no need to mess with /system again.